Even though network nodes in the IP Multimedia Subsystem (hereinafter IMS) core network should have a very high availability, some maintenance downtime and occasional failures are unavoidable. Therefore, a set of standardized procedures have been specified for IMS restoration. In this respect, 3GPP TS 23.380 Section 5 “Recovery after P-CSCF failure” covers the case of service interruption of a Proxy Call Session Control Function (hereinafter P-CSCF), by involving entities of a Policy and Charging Control (hereinafter PCC) architecture to convey the P-CSCF address through the so-called Rx and Gx interfaces.
The invention thus involves entities of a PCC architecture in accordance with 3GPP TS 23.203 for Evolved 3GPP Packet Switched domain, including both 3GPP accesses (GERAN/UTRAN/E-UTRAN) and Non-3GPP accesses. For the purposes of the present invention, the PCC architecture comprises an Application Function (hereinafter AF), a Policing and Charging Rules Function (hereinafter PCRF), and a Policing and Charging Enforcement Function (hereinafter PCEF). Particularly applicable where a PCC architecture cooperates with an IMS core network, the P-CSCF of the IMS core network behaves as, or includes, the AF of the PCC architecture.
At present, the existing IMS Restoration procedure as defined in 3GPP TS 23.380 is prepared by an AF node, namely the P-CSCF, receiving from a user's equipment (hereinafter UE) an IMS registration and passing the P-CSCF address to the PCRF and from the latter to the PCEF, in order to apply a so-called P-CSCF monitoring procedure by the PCEF and to trigger a PDP Context update/Bearer update where the P-CSCF is found to be unavailable by the PCEF.
That is, the PCEF cannot apply the P-CSCF monitoring procedure according to recent standards unless the PCEF receives the corresponding P-CSCF address from the PCRF.
Moreover, the current solution as stated by the 3 GPP technical specification has a number of limitations that can be summarized as being only applicable if all the entities involved, namely P-CSCF, PCRF and PCEF, are adapted to carry out such IMS Restoration, what is not the case for PCC deployments older than those for Release 9.
More specifically, the presently standard solution requires that the P-CSCF supports this functionality, is enabled to negotiate the feature with the PCRF and, if supported, provides additional data in the Rx interface. Moreover, the presently standard solution requires that the PCRF supports this functionality, is enabled to negotiate the feature with both P-CSCF and PCEF and, if supported by both, handles additional data in both Gx and Rx interfaces.
Obviously, all this requires extra signalling to provide this functionality through the Gx interface for those solutions where PCC rules for SIP signalling are statically configured in the PCEF; and, consequently, the IMS Restoration procedure as required by 3GPP technical specifications cannot be provided by PCC deployments not upgraded to Release 9.